This invention relates to ink jet recording systems, method and apparatus. In particular, this invention relates to sensing the location of the fluid drops while they are in flight.
Fluid drop recording systems including mechanical, electrical, electrostatic and magnetic deflection techniques invariable create a record by depositing drops in a given pattern on a record medium, i.e. at the various pixel positions within a raster pattern. A drop is placed at a desired pixel location by either moving a carriage holding the drop generator relative to the record, by magnetically or electrically deflecting the drop to the pixels or a combination of the foregoing techniques.
A sensor for detecting the position of the drop either in flight or upon impact is valuable for controlling droplet velocity, phasing and alignment to the raster pattern. U.S. Patents to Naylor et al No. 3,886,564; Carmichael et al, No. 3,992,713; and Hill et al, No. 3,769,630 and the patents cited therein are exemplary of various sensors and their application. The disclosures of those patents are incorporated herein. In electrostatic recorders the drops are sensed electrically either by impacting an electrode or by charge induction. Magnetic recorders, of course, may use magnetic flux coupling to detect a drop. Optical detection of drops is known. The U.S. Patent to Kuhn et al, No. 3,907,429 is an example of the use of light to detect the velocity of the drop. An article by G. J. Fan in IBM Technical Disclosure Bulletin, Vol. 16, No. 3 of August, 1973 discloses an optical fiber positioned to collect the light from a LED when not interrupted by the flight of drops.
The various prior art sensors do not have good signal to noise ratios and are subject to crosstalk, i.e. are frequently unable to differentiate from other drops in its own or an adjacent stream. Also, the prior art sensors are difficult to implement in recorders due to the small space available in devices where the drop size ranges from about 10 to 1,000 microns. They are also subject to contamination by the drop itself, i.e. the ink.
Accordingly, it is a principle object of this invention to overcome the limitations of prior art fluid drop sensors.
Another object of this invention is to measure or detect the position of small objects in the 10 to 1,000 micron diameter size range whether fluids, solids, spheres or cylinders.
Yet another object of the invention is to use a plurality of sensors in an electrostatic fluid drop recorder wherein each nozzle in an array of nozzles records along a segment of a row of pixels in a raster pattern by electrostatic deflection of the drops. The sensors are used to electrically calibrate each nozzle to accurately align the segments composed by each nozzle to the ideal pixel locations in a raster. This alignment process is also referred to as stitching.
Even a further object of the invention is to provide the sensor for detecting or measuring a fluid drop position independent of its electrostatic charge or magnetic properties.
Still another object is to detect the location of a drop in a system wherein the drop generator and target are moved relative to each other. In other words, it is an object to devise a "bulls eye" for a moving drop generator, moving target or both to test its accuracy at drop placement.
It is also an object of the present invention to devise means for sensing the presence of a drop along one, two or three axis of an orthogonal x, y, z coordinate system.